1. Field of the Invention
This invention relates to power management within integrated circuits, and more particularly to monitoring activity for different functional units of an integrated circuit for power management.
2. Description of the Related Art
Some of the factors contributing to overall power consumption within an integrated circuit are dynamic power consumption, (power consumption caused by capacitive charging during the switching of a transistor) and static power, (power caused by leakage current through a transistor in the off state). The power and thermal constraints placed on modern semiconductor devices are rapidly becoming a limiting factor to the performance and functionality available in a single device. VLSI (Very Large Scale Integration) and extreme high clock speeds have become the norm. The high clock speeds are to drive the integrated circuit faster to perform its respective job faster, and the faster the integrated circuit operates the more the more power it typically consumes. Integrated circuits must also efficiently dissipate the heat generated from consuming power during operating. If the heat is not efficiently dissipated, then the semiconductor material that makes up the integrated circuit may continue to increase in temperature which could lead to malfunction, device damage, thermal runaway, etc. Thermal runaway is where the device will continue to increase in heat and power consumption until it eventually and permanently fails. Thermal problems may lead to actual breakdown of one or more of the device junctions in the semiconductor material.
Integrated circuits now contain more semiconductor devices than ever before due extreme integration. The more semiconductor devices that are contained in an integrated circuit for example, the greater the power consumption and need for efficient heat dissipation. Even with all of the technological advances made in integrated circuits, problems still arise from an increasing need to miniaturize and increase the density in already crowded semiconductor die. Due to miniaturization within an integrated circuit, features are finer. Increasing density means that there is more combined heat that must be dissipated in a smaller area.
Power supply size is proportional to the amount of power that must be supplied. Thus, lower power requirements lead to smaller power supplies. Where the application dictates the use of a battery for a power source or an alternate power source, the circuitry may sustain an increased battery life if power consumption is reduced. Likewise, in an application where the power source is contained on the same printed circuit board as the system logic, less PCB real estate may be necessary because the physical size of the power source is reduced.
Because today's integrated circuits actually have more functionality, they have a denser population and dissipate more heat per square inch than ever before, requiring new and innovative ways to dissipate this additional heat faster. If power consumption and heat related problems cannot be addressed, a device may have to be operated at a lower frequency or at a lower voltage or include fewer devices than desired to reduce power consumption and avoid thermal problems.
Excessive heat also affects the characteristics of other non-silicon materials used in the design and assembly of electronic equipment today. Due to cost-reducing steps that may be taken, some materials that are used in today's equipment may not withstand the excessive heat generated within that equipment. For example, certain types of plastic, rubber, vinyl, and adhesive may deteriorate and/or warp when exposed to excessive heat, possibly affecting the fit, form or functionality of the equipment. Thus, there is a need to dissipate heat faster and lower the average operating temperature of a device. Many methods are used to improve heat dissipation and all are effective to some degree.
Problems associated with excessive heat may be addressed by using one or more heat sinking and cooling techniques at the IC (integrated circuit) and component level. These techniques may solve some of the problem, but may not lend themselves to every application. One example of an IC level cooling technique is the process of making certain leads that extend out of the IC much larger than others so that the enlarged leads effectively increase the square area of the total heat-transferring real estate, thus conducting heat away from the IC faster. Although enlarging the leads on an IC may provide some heatsink capability, this technique may not apply to all package types and there are physical limitations to the size the leads may be. Heat-transferring characteristics are directly proportional the cross sectional area of a heat transferring device. Heatsinks may be mounted to an integrated circuit, often with the help of thermal transfer compound and a clamp. If more cooling is required, a fan may be mounted to the heatsink to improve heat dissipation. Using two methods in conjunction, for example, mounting a heat sink to an integrated circuit and mounting a fan on top of it, is a common practice. However, heatsinks and fans generally take up valuable space and add cost in a system.
Another method may be to attach a thermoelectric semiconductor device called a frigistor to an integrated circuit or a bank of integrated circuits. Due to the Peltier effect, the frigistor will refrigerate the circuitry to a desired temperature. When the electric current flows form the negative element to the positive element, the top electrode of the N-type junction moves from a low energy level to a high energy level, thereby lowering the temperature. Conversely, the temperature of the lower electrode rises because it passes form a high energy level to a low energy level. The temperature may be controlled many ways, most common of which is using a thermocouple and a switching circuit that turns the cooling device on and off. These devices may not be cost effective in some designs where cost is an issue.
Many conventional power management techniques may become inadequate in designs where space constraints are present within the equipment. Power consumption may become more of an issue because of the physical size of the power supply and battery life. Thus, reducing the amount of power that is actually consumed may be more desirable then trying to figure out how to cool integrated circuits by using larger and larger heat-sinking apparatuses.
Power management software is one method that may be used to reduce power at the system level. Power management software is intended to reduce the power consumed by high power consumption device in a system, such as a handheld or laptop device.
One conventional technique used to reduce power consumption within an integrated circuit is to design as much of the functional block of the IC as possible to operate on lower operating voltages, which reduces power consumption. While this technique may be effective, it may only be feasible in some applications. Other parts of the circuitry may need increased voltage to fulfill circuitry requirements, thus requiring multiple power sources. For example, this may be accomplished by using an integrated circuit and an output driver coupled to a first voltage supply and a level shifter circuit coupled to a second voltage supply.
Another method of reducing power consumption is to operate an integrated circuit at a lower frequency. However, performance goals may not be met at a lower frequency. Other methods to reduce power consumption may be to reduce the functionality of the circuitry so that fewer transistors are used. Even though this type of sacrifice reduces power consumption, it may result in a design that does not meet performance and functionality goals.